Generally, products are formed by casting, die-casting, stretching, and extrusion. The first two types can do more complex processes, while the latter two types have certain production limitations.
Aluminum electrolysis production process
Modern aluminum industry production uses cryolite-alumina molten salt electrolysis method. Molten cryolite is the solvent, and aluminum oxide is the solute that is dissolved. Carbon is used as the anode (prebaked anode block), and aluminum liquid is used as the cathode. After direct current is passed through, at 940°C to 970°C, electrolysis is performed on both poles of the electrolytic cell. Chemical reaction, electrolysis. The anode products are mainly carbon dioxide and carbon monoxide gas, but they contain a certain amount of harmful gases such as hydrogen fluoride (HF) and solid dust. The anode gas must be purified to remove harmful gases and dust before being discharged into the atmosphere. The cathode product is aluminum liquid. The aluminum liquid is extracted from the tank through a vacuum ladle and sent to the casting workshop. After purification and clarification in the mixing furnace, it is poured into aluminum ingots or produced into wire blanks, profiles, etc. The production process flow chart is as shown in Figure 3-1:
Alumina fluoride aluminum carbon anode
Direct current
Anode gas
Aluminum Liquid
The waste gas is evacuated and returned to
Electricity
Solution
Trough
Fluorine-carrying alumina
Aluminum ingots
Alloys, wire blanks
Figure 3-1 Aluminum electrolysis production process flow chart
Section 2 Raw and auxiliary materials for aluminum electrolysis production
1. Aluminum oxide:
Alumina is usually called "aluminum oxide". It is a white powder with a melting point of 2050°C, a boiling point of 3000°C, and a true density of 3.6g/cm3. It has good fluidity, is insoluble in water, and can be dissolved in molten cryolite. It is the main raw material in aluminum electrolysis production.
The role of alumina in electrolytic production is: a. Continuously replenish the aluminum ions in the electrolyte to keep its concentration within a certain range to ensure the continuous progress of electrolytic production; b. Alumina covering It can play a good thermal insulation role on the electrolyte shell surface and cover the oxidation of the anode carbon block; c. Act as an adsorbent in the flue gas purification system to adsorb hydrogen fluoride (HF) gas in the anode gas.
In terms of chemical purity, the impurity content and moisture content in alumina are required to be low. Because those oxides in alumina that have a potential positive to that of aluminum, such as SiO2 (silicon dioxide) and Fe2O3 (iron oxide), will be reduced by aluminum during the electrolysis process, or will precipitate at the cathode in preference to aluminum ions. The precipitated silicon and iron enter the aluminum and reduce the grade of aluminum. Those oxides with a potential negative than the aluminum element, such as Na2O and CaO (calcium oxide), will decompose cryolite. First, it will cause the consumption of fluoride salts. Second, it will increase The hydrogen content in aluminum, third, produces hydrogen fluoride gas, which pollutes the environment. P2O3 (phosphorus pentoxide) affects current efficiency. The chemical composition requirements of alumina are shown in Table 3-1.
Table 3-1 my country’s alumina quality standards (YB814-75)
Grade
Code chemical composition (%)
Al2O3 Content
No less than impurity content no more than
SiO2 Fe2O3 Na2O Caustic soda
First class
Second class
Level 3
Level 4
Five poles
Level 6 Al2O3—1
Al2O3—2
Al2O3—3
Al2O3—4
Al2O3—5
Al2O3—6 98.6
98.5
48.4
98.3
98.2
97.8 0.02
0.04
0.06
0.08
0.10
0.15 0.03
0.04
0.04
0.05
0.05
0.06 0.50
0.55
0.60
0.60
0.60
0.70 0.8
0.8
0.8
1.0
1.0
1.2
Except for chemical composition , the central blanking prebaked tank also has special requirements for the physical properties of alumina:
a. It has small water absorption and good solubility in the electrolyte;
b. The particle size is suitable, with little flying loss when feeding, and can be tightly covered on the anode carbon block to prevent the anode from oxidizing in the air;
c. It has good thermal insulation performance and high activity, so it can effectively absorb HF gas.
d. Angle of repose: 35~38°.
According to the different physical properties of alumina, it can be divided into three categories: sandy, powdery and intermediate. Table 3-2 below lists the characteristics of the three types of alumina.
Table 3-2 Characteristics of different types of alumina
Alumina type Angle of repose (°) Ignition loss (%) Cumulative (%)
-44μm -74μm
Sandy
Intermediate
Powdery 30
40
45 1.0
0.5
0.5 5 -15
30-40
50-60 40-50
60-70< /p>
80-90